The functions enabled the cars to emit NOx pollutants up to 10 times higher than legally permitted levels, Bild am Sonntag said.

The paper cited emails from the automaker’s engineers questioning whether the software functions were legal.

A spokesman for Mercedes owner Daimler declined to comment on the content of the documents, saying the automaker was fully cooperating with the U.S. authorities and had agreed upon strict confidentiality with the Department of Justice.

Daimler faces ongoing investigations by U.S. and German authorities into excess diesel emissions. It has said investigations could lead to significant penalties and recalls.

“The authorities know the documents and no complaint has been filed,” the spokesman said. “The documents available to Bild have obviously selectively been released in order to harm Daimler and its 290,000 employees.”

There has been growing scrutiny of diesel vehicles since Volkswagen admitted in 2015 to installing “defeat” software on 580,000 U.S. vehicles that allowed them to emit up to 40 times legally allowable emissions while meeting standards when tested by regulators. The cars had software that switched off performance-reducing emissions control systems during laboratory testing.